1. Field of the Invention
The present invention relates to a method for controlling a transmission control protocol (hereinafter, referred to as ‘TCP’) window size in an asynchronous transfer mode (hereinafter, referred to as ‘ATM’) network, and in particular to a method for determining a TCP congestion window size by using an explicit rate (hereinafter, referred to as ‘ER’) value in a resource management (hereinafter, referred to as ‘RM’) cell.
2. Description of the Background Art
In general, an available bit rate ABR service has been developed to support a data application in the ATM network, and the TCP is the most widely-used transport level protocol in a currently-used data network.
A TCP window-based flow control is a method for predicting a packet loss by employing an acknowledgement (ACK) signal transmitted from a receiving side. The aforementioned method can detect a congestion state of the network only when the packet loss is generated. Sometimes, the retransmission may be unnecessarily performed by mistakenly predicting the packet loss.
Here, a method for predicting the packet loss detects the congestion state of the network by predicting the packet loss by using a TCP timeout. However, this method has a disadvantage in that a degree of the congestion state of the network cannot be measured because a feedback of the TCP is provided merely by the receiving side TCP.
As described above, the TCP window-based flow control predicts the packet loss, and thus increases/decreases the window size. However, the congestion state of the network cannot be precisely evaluated by a simple increase/decrease of the window size. Accordingly, the window size may exceed an allowable size in the network. At this time, the packet loss and the resultant retransmission are generated, and thus the increase/decrease of the window size and retransmission are repeated.
In addition, since a delay sharply varies according to the network state on the TCP over the ABR service, a retransmission timeout (hereinafter, referred to as ‘RTO’) value also increases. In case the packet loss is generated, the loss may be detected after the RTO. As a result, the level of performance ability considerably reduces. According to the fast-retransmission algorithm of the TCP-Reno (“TCP/IP Illustrated Volume 1: The Protocols” by W. Richard Stevens (Addison-Wesley, 1994), more than a half of the packet loss can be detected before the RTO, and according to the method suggested by the TCP-Vegas (Lawrence S. Brakmo and Sean W. O'Malley, “TCP Vegas: New Techniques for Congestion Detection and Avoidance”, SIGCOMM '94 Conference on Communications Architectures and Protocols, pp. 24–35, October 1994), more than a half of the residual packet loss can be detected in advance, thereby reducing the number of cases of waiting the RTO. Nevertheless, the decrease and recovery of the window size resulting from the retransmission reduce a TCP throughput.
In the conventional TCP over the ABR service, a bandwidth which can be used by the TCP is dependent upon time. Accordingly, a fast recovery to the bandwidth and transmission by a linear increase from the time are not significant.